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Cyclic and Cubic Organophosphonates of Gallium and Their Relationship to Structural Motifs in Gallophosphate Molecular Sieves.

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Cyclic and Cubic Organophosphonates of
Gallium and Their Relationship to Structural
Motifs in Gallophosphate Molecular Sieves""
M a r k R . Mason,* Mark S. Mashuta, and
John F. Richardson
The synthesis of the large-pore molecular sieve cloverite"] has
sparked the search for new gallophosphate (GaPO,) materials
with potential catalytic and sorptive properties. This effort has
resulted in the preparation of several unique GaPO, phases
having diverse structures with no aluminophosphate or aluminosilicate counterpart.12-'I The use of fluoride as a mineralizing
agent has been instrumental for the synthesis of several of these
phases. Incorporation of fluoride in the resulting product has
led to secondary building units (SBLJS)[~]
that contain p2-F
bridges between gallium atoms,[" 81 as well as encapsulated
fluoride in double four-rings (D4Rs) as found in cloverite,
ULM-5,[91and gallophosphate-A.['O] Although it was initially
thought that fluoride has a strong propensity to form D4R
structures in GaPO, phases, the finding of SBUs with p2-F
bridges and the finding that fluoride is not always incorporated
into the final GaPO, product[' 'I raises interesting questions
concerning the role of fluoride as a template and the potential
diversity of undiscovered structural motifs in the fluoride/
GaPO, system.
We have initiated the synthesis of derivatives of gallophosphate SBUs that are soluble in organic solvents in order to
probe interactions with fluoride and to employ the derivatives
as potential precursors to new GaPO, materials. Our initial
target molecules were those with a cubic Ga4P4OI2 core
analogous to the D4Rs in cloverite, ULM-5, and gallophosphate-A. The targeted Ga,P,O,, core is isoelectronic and structurally related to the Si,O,, core of the octameric silasesquioxanes [RSiO, ,J8 ,[I2, 1 3 ] and structurally related to the A1,Si,O, ,and Ga,Si,O, cores of soluble alumin~siloxanes,~'~~
'I
aluminosilicates,[' and gallosiloxanes,['6J which have been introduced by Roesky et al. as models of, and potential precursors
to, zeolitic materials. The Ga4P4OI2core is also analogous to
the AI,P,O,, cores of aluminophosphatesf"] and aluminophosphonates['8. 19] that are soluble in organic solvents. We report
here on the synthesis and characterization of the cyclic gallophosphonate l and the first gallophosphate D4R derivative 2.
[1Bu,Ga(~(,-O,P(OH)Ph)l, 1
[rBuGa(pc,-O,PPh)], 2
Equimolar reaction of tBu3Ga and phenylphosphonic acid
readily yields compound 1 as a white crystalline solid in 79%
yield. The ' H NMR spectrum for 1 shows a 2:l ratio of tertbutyl to phenyl substituents consistent with the formula
[tBu2Ga(p2-0,P(OH)Ph)l,. The presence of unconverted hydroxyl substituents on phosphorus is confirmed by a broad OH
resonance centered at 6 = 8.00 in the 'HNMR spectrum, as
well as a broad intense 0 - H stretch centered at 3300 cm-' in
the IR spectrum. Elemental analysis is also consistent with the
[*] Prof. M. R Mason, Dr. M. S . Mashuta, Prof. J. F. Richardson
Department of Chemistry and Center for Chemical Catalysis
University of Louisville, Louisville, KY 40292 (USA)
Fax: Int. code +(502) 852-8149
e-mail- mrmasoOl (a homer.louisville.edu
I**]
This work was supported by the Donors of The Petroleum Research Fund,
administered by the American Chemical Society (Grant 29723-G3). High-resolution m a s spectrometric analyses were provided by the Nebraska Center for
Mass Spectrometry. Elemental analyses were performed by Schwarzkopf Mlcroanalyticai Laboratory. Inc., Woodside, N Y
A n g n i . Chem. fnr. Ed. €ng(. 1997, 36. No. 3
formulation [tBu,Ga(p2-O2P(0H)Ph)I,, and high-resolution
mass spectrometry confirms a dimeric species (n = 2) in the gas
phase. Dimeric structures with eight-membered Ga2P,0, rings
have previously been proposed for phosphinates of gallium,
[R,Ga(p,-O,PR;)], (R = Me, Et; R = Me, Ph, F. Cl), on the
basis of spectroscopic data,[20-231and confirmed in the solid
state by X-ray crystallography for [ t B ~ ~ G a ( p , - 0 , P P h ~ ) 1 , [ ~ ~ '
and [(CH,),Ga(pz-0,PPh2)]2.[251
The molecular structure of 1 is shown in Figure 1. The centrosymmetric Ga,P,O, ring comprises two p2-v2-02P(OH)Ph
units bridging distorted tetrahedral gallium centers. All angles
Figure 1. Crystal structure of 1 (ORTEP drawing). Thermal ellipsoids are drawn at
the 50% probability level, and hydrogen atoms, except for hydroltyl hydrogens, are
omitted for clarity. Selecred bond lengths [A] and angles ['I. Gal - 0 1 1.944(4),
Gal - 0 2 1.917(4), P1-01 1.490(4), P1-02* 1.483(4), P1-03 1.556(5); 01-Gal-02
102.8(2), C7-Gal-Cll 130.2(3), 01-P1-02* 115.4(3), 01-P1-03 111 0(3), Gal-01P1 142.3(3), Gal-02-P1* 157.8(3).
at gallium lie between 102.6(3) and 107.7(2>0except for the large
C-Ga-C angle of 130.2(3)". Gallium-oxygen distances
(1.944(4), 1.917(4) A) and intra-ring P - 0 distances (1.483(4),
1.490(4) A) are comparable to those in the related heterocycles
[tBu2Ga(p2-02PPh,)], (Ga-0 1.950(8), 1.969(7) A; P - 0
1.485(8), 1.497(8) A) and [(CH,),Ga(p~-0,PPh2)1, (Ga-0
1.9384(12), 1.9295(12) A; P - 0 1.5204(12), 1.5095(12)A).
The most intriguing structural feature for 1 is the trans orientation of the hydroxyl substituents at phosphorus in the solid
state despite the observation of a 50/50 mixture of cis and trans
isomers in solution by multinuclear ('H, 13C, 31P)NMR spectroscopy. To explain this observation, we suggest a cis- trans
equilibrium in solution with preferential crystallization of the
trans isomer. This proposal is consistent with the thermolysis of
1 in solution, which results in the high-yield fusion of two
Ga2P20, rings to form the cubic Ga,P,O,, core of 2, as described below. The high yield observed is consistent with a cistrans isomerization; however, only the cis isomer converts to the
cubic compound 2. The trans isomer should yield only polymeric products. Further details of the proposed isomerization of 1
and related compounds are under investigation.
The thermolysis of 1 in diglyme under reflux yields 2 as a
crystalline white precipitate in 88 % yield. Thermolysis in lower
boiling solvents such as toluene or xylene is precluded by the
thermal stability of 1. Compound 2 exhibits a 1 :3 ratio of tertbutyl to phenyl substituents by 'H NMR spectroscopy. Both
'HNMR and IR spectroscopic data confirm the absence of
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hydroxyl substituents on phosphorus. Multinuclear NMR spectrospcopic data show 2 to be highly symmetric. These data
and elemental analyses are consistent with the formulation
[rBuGa(p,-O,PPh)], . Mass spectrometric data confirm that 2
is a tetramer (n = 4) in the gas phase, and all evidence suggests
that 2 remains a tetramer in solution.
The tetrameric structure of 2 has also been confirmed in the
solid state by X-ray crystallography. The triclinic unit cell contains two independent molecules of the complex, each with the
same overall geometry, but with slight variations in bond
lengths and angles. One of the independent molecules exhibits
greater distortions than the other,[261but average distances and
angles for the two molecules are comparable. The following
discussion of the molecular structure is limited to the structural
parameters of the least distorted molecule (Figure 2).
cycles noted above, and those in gallophosphate materials. Gallium-oxygen distances (1.827(7)-1.858(7) A; av 1.84 A) are
significantly shorter than those in I, [(CH,),Ga(p,-02PPh2)1,,
and [tBu,Ga(p,-O,PPh,)], (av 1.93, 1.93, and 1.96 A, respectively), but are in the range observed for four-coordinate gallium in gallophosphates.
The comparison of 2 with the D4Rs in cloverite reveals that
the two have comparable G a - 0 and P - 0 distances, but the
D4R of cloverite has smaller P-0-Ga angles (132.9- 141.3') and
larger 0 - G a - 0 angles (114.7-121.3") than those in 2 (146.8(5)155.6(6) and 102.1(4)-104.8(4)", respectively). The larger 0G a - 0 angles in doverite can be attributed to the encapsulated
fluoride ion, which forces a trigonal-bipyramidal coordination
at gallium in which three p,-0x0 ligands are situated in the
equatorial plane. On average, intracage diagonal Ga- P distances are somewhat shorter in cloverite (5.42A) than in 2
(5.58 A). The shorter distances arise from slight inward puckering of the gallium atoms to maximize bonding with the encapsulated fluoride ion. The overall similarities of the cage unit and
the inner dimensions of the Ga,P,O,, core of 2 with that of the
D4Rs of cloverite suggests that encapsulation of fluoride in 2
should be feasible. Efforts to affect this encapsulation are currently in progress.
Experimental Sect ion
Figure 2. Top: Crystal structure of one of the independent molecules of 2 (ORTEP
drawing). Bottom: Ga,P.,O,, core of 2 with only ips0 carbon atoms shown for
clarity. Thermal ellipsoids are drawn at the 40% (top) and 50% (bottom) probability levels. Hydrogen atoms are omitted for clarity. Selected bond lengths [A] and
angles ["I: Ga8-019 1.852(7), Ga8-020 1.827(7), Ga8-023 1.827(7), P7-018
1.493(7), P7-019 1.486(7), P7-022 1.495(8); 019-Ga8-020 103.4(4), 019-Ga80 2 3 104.5(4), 020-Gag-023 103.7(4), Ga8-019-P7 146.8(5), Ga8-023-P6 1st . l ( S ) ,
Ga8-020-PS 155.6(6), 018-P7-019 112.4(5), 018-P7-022 112.4(5), 019-P7-022
112.0(5).
The structure of 2 is composed of a cubic Ga4P40,, core in
which gallium and phosphorus atoms occupy vertex positions,
and pz-oxo bridges form along the edges. This core is analogous
to the D4R building blocks in cloverite, ULM-5, and gallophosphate-A. Gallium and phosphorus atoms reside in distorted
tetrahedral environments; the angles at gallium and phosphorus
range from 102.1(4)- 116.5(5)" and 105.8(5)- 113.1(6)",respectively. Phosphorus-oxygen distances (1.478(8)-1.512(8) A) are
normal by comparison to those in 1, those in the related hetero240
0 VCH Verlamgesellschafl mbH, 0-694Sf
Wernherm, 1997
All reactions were performed in an atmosphere of purified nitrogen by using standard Schlenk line techniques. Low-resolution mass spectra m/z values are reported
for the predominant peak within the isotope pattern.
1: A solution of PhP(O)(OH), (l.S8g, 10.0mmol) in T H F (15mL) was added
dropwise to a stirred solution of tBu,Ga 1271 (2.41 g, 10.0 mmol) in toluene (25 mL)
and THF (5 mL). The resulting clear solution was heated to reflux for 1.5 h. The
volume of the solution was reduced in vacuo and the solution was cooled at - 20 'C
overnight to produce clear, colorless crystals of 1. The crystalline product became
white upon isolation by filtration and briefdrying in vacuo. The filtrate was concentrated and cooled to yield a second batch of product. Yield of 1as a disolvate: 3.25 g
(3 93 mmol, 79%). 'H NMR (500 MHz, CDCI,, TMS). 6 = 8.00 (br, 2H, O H ) ,
7.84 (m, 4H, ortho), 7.45 (m. 2H, para), 7.41 (m, 4H, mero), 3.58 (m, 8H. OCH,.
(THF)), 1.73 (m.8H. CH,CH,. (THF)), 1.16(s, 9H. I B U ,cisisomer), 1.01 (s, 18H.
rBu. rran.7 isomer). 0.88 (s. 9H, rBu, cis isomer); '3C{iH) NMR (125.5 MHz,
CDCI,, TMS): 6 = 132.98 (d. 'J(P,C) = 196.9 Hz, ipso), 132.60 (d, 'J(P,C) =
198.0 Hz, ip.so), 131.30 (hr, para), 131.22 (br,para), 131.07 (d, 'J(P,C) =10.2 Hz,
orlho), 128.07 (d, ,J(P,C) =15.2 Hz, mera), 128.04 (d, 'J(P,C) =15.2 Hz, meta),
67.79 (s, OCH,, (THF)), 29.83 (s, CH,), 29.78 (s, CH,), 29.71 (s, CH,), 25.32
(s, CH,CH,, (THF)).22.83 (s, C(CH,),), 22.72 (s, C(CH,),); ''P('H} NMR
(Yv): 625 (40)
(121.5 MHz, CDCI,, 85% H3P0,): 6 =7.1 (s), 6.8 (s). MS (EI):
[M' -tBu], 567 (100) [M+- fBu-rBuH]. HR-MS (EI): m/z for
C,,H,,0,69Ga,Pz
[M' - rBu]: 623.0765 (calcd 623.0734). Anal. calcd for
C,,H,,O,Ga,Pz:
C 52.33. H 7.81. P 7.50. found: C 52.02, H 7.80, P 7.63.
2 . A solution of 1 (2.25 g. 2.72 mmol) in diglyme (50 mL) was heated to reflux for
6 h during which time a white precipitate formed. Precipitation of the product was
completed by cooling ( - 20'C) the solution for one day. The white product was
isolated by filtration. washed with diethyl ether (2 x 20 mL), and dried in vacuo.
Yield of 2 : 1.36 g (1.20 mmol, 88%). Colorless, cubic crystals for X-ray analysis
were grown from a slowly cooled hot diglyme solution. 'H NMR (500 MHz, CDCI,, TMS): 6 =7.82 (dd, 'J(P,H) = 14.3, ,J(H,H) =7.0 Hz, 2H, ortho), 7.48 (td,
3J(H,H) = 7.4, 'J(P, H) = 1.4 Hz, lH,paru), 7.43 (m, 2H, mrra), 1.02 (s, 9H, CH,),
"C('H} NMR (125.5 MHz, CDCI,, TMS). 6 =132.87 (d, 'J(P,C) = 212.2Hz.
ipso), 130.98 (br. para), 130.51 (d, 'JJ(P,C) =10.2Hz, orrho), 127.96 (br, mera),
28.79 (q, 4J(P,C) =13.2Hz, CH,). 21.62 (br, C(CH,),); "P{'H} NMR
(121.5 MHz, CDCI,. 85% H,PO,): d = 3.2 (s). MS (EI): m/z (%): 1075 (100)
[M' - rBu]. Anal. calcd forC,,H,,0,,Ga,P4:
C 4 2 45, H 4.99, P 10.95, Ga 24.64;
found: C 42.38, H 5.06. P 10.84. Ga 24.96.
monoclinic, C2/c (no.l5), a =
Crystal structure data for 1: C,,H,,O,Ga,P,,
20.234(7), h = 13 554(3), c = 16.437(4)A, p = 95.52(3)", V = 4486(1) A,, 2 = 4,
pralcd= 1.22 gcrn',, T = 295 K. All measurements were made on an Enraf-Nonius
CAD4 diffrdctometer with graphite-monochromated Mo,, radiation. Calculations
were performed by utilizing the teXsan [28] crystallographic software package The
structure was solved by direct methods (SIR-92) and expanded by using fourier
techniques. The disordered T H F solvate molecule was modeled by using isotropicalIY refined non-hydrogen atoms. Hydrogen atoms were located by difference maps
and includes but nor refined. Of 3310 data collected (maximum 20 = w, M~,,,
=13.13cm-'), 3228 were unique. The final residuals for 173 parameters refined
R = 0.054 and R, = 0 . 0 ~ ~ .
against 2890 unique data with 1 > 3 ~ ( 1were
)
0570-0833f9713603-0240$ 1 5 . 0 0 i ,2510
Angen. Chem. Inr Ed. Engl. 1997, 36, No. 3
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Crystal structure data for 2: C,,H,,O,,Ga,P,,
triclinic, PT (no. 2), a =15.647(2),
h = 22.325(3), c =14.852(4) A, a = 94.91(2), B = 90.17(2), y = 83.53(1)", V =
5136(1) A', Z = 4, pCllcd= 1.463 gcm-', T = 296 K. Instrumentation and software
were as noted for 1. The structure was solved by Patterson methods and expanded
by using fourier techniques. Hydrogen atoms were included but not refined. Of
18771 data collected (maximum 26 = SO", Mo,., p = 22.52 cm-'), 18033 were
unique. The final residuals for 1082 parameters refined against 8078 unique data
with I > 30(I) were R = 0.053 and R, = 0.054. Crystallographic data (excluding
structure factors) for the structures reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication no.
CCDC-100024 Copies of the data can be obtained free ofcharge on application to
The Director. CCDC, 12 Union Road, Cambridge CB2 1EZ. UK (fax: Int.
code + (1 223) 336-033; e-maii deposit@,chemcrys.cam.ac.uk).
Received August 21, 1996 [Z9480IE]
German version Angew Chem 1997, 109, 249-251
-
Keywords: cage compounds . gallium gallophosphates * mesoporosity
[l] M. Estermann. L. B. McCusker, C. Baerlocher, A. Merrouche, H. Kessler,
Nuturr 1991. 352. 320-322.
[2] A. M. Chippindale, R. I. Walton, C. Turner, J Chem. Soc. Chem. Commun.
1995. 1261 -1262.
[3] W Tieli. Y. Guangdi, F. Shouhua, S. Changliang, X. Ruren, J Chem. Soc.
Chem Commun. 1989.948-949.
[4] Y. Guangdi, F Shouhua, X. Ruren, J. Chem. SOC.Chem. Commun. 1987,12541255.
(51 J. B. Parise, J Chem SOC.Chem. Commun. 1985, 606-607.
[6] W. M. Meier, D. H. Olson, Atlas of Zeolite Structure Types, 3rd ed., Butterworth- Heinemann. 1992, p. 6.
[7] X. Yin. L. F. Nazar, J Chem. SOC.Chem. Commun. 1994, 2349-2350.
[8] T LOiSedu. R. Retroux, P. Lacorre, G . Ferey, J Solid State Chem. 1994, I /I,
427 436.
[9] T. Loiseau. G. Ferey, J SolidStute Chem. 1994, / / I , 403-415.
[lo] A. Merrouche, J. Patarin, M Soulard, H. Kessler, D. Anglerot, Synrh. Microporous Muter. 1992. /, 384-399.
s 1 1 T. Loiseau, D. Riou, M. Licheron, G. Ferey, J. Solid State Chem. 1994, if /,
397 -402.
M G. Voronkov. V. I. Lavrentyev, Top. Curr Chem. 1982, /02, 199-236.
F. J Feher, T. A. Budzichowski, Polyhedron 1995,/4, 3239-3253.
V Chandrasekhar, R. Murugavel, A. Voigt, H. W. Roesky, H.-G. Schmidt, M.
Noltemeyer, Or,eunometullics 1996, 15, 918-922.
M. L. Montero. A. Voigt, M. Teichert, I. Uson, H. W. Roesky, Angew. Chem.
1995, 107.2761 -2763; Angew Chem. In!. Ed. Engl. 1995, 34, 2504-2506.
A . Voigt, R. Murugavel, E. Parisini, H . W. Roesky, Angew. Chem. 1996, 108,
823-825; Angeu Chem. Int. Ed. Engl. 1996,35,748-750.
M. R. Mason, R. M. Matthews, M. S. Mashuta, J. F. Richardson, Inorg.
Chem. 1996, 35. 5756-5757.
A . M . Perkins, R. M. Matthews, M. S. Mashuta, J. F. Richardson, M. R. Mason. Abstracts ( J / Pupers, 212th National Meeting of the American Chemical
Society. Orlando. FL, 1996; INOR 146.
Y Yang, H.-G. Schmidt, M. Noltemeyer, J. Pinkas, H. W. Roesky, J Chem.
Sot.. Dalton Trans. 1996, 3609- 3610.
G. E. Coates, R. N. Mukherjee, J. Chem. Sot.. 1964, 1295-1303.
I. Weidlein, B. Schaible, Z . Anorg. Allg. Chem. 1971, 386, 176-184.
H. Olapinski, B Schaible, J. Weidlein, J Orgunornet. Chem. 1972,43,107- 117.
B. Schaible, J. Weidlein, J Orgunornet. Chem. 1972, 35, C7.
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1996, 15, 391 -402.
F. E Hahn. B. Schneider, FFW. Reier, Z Nururforsch. B 1990, 45, 134-140.
The ranges and averages of selected bond lengths [A] and angles ["I for the more
distorted independent molecule of 2 are: G a - 0 1.822(7)-1.869(7) (av 1.85),
P - 0 1.489(7) - 1.520(7) (av 1.51), P-0-Ga 135.6(5)-175.2(6) (av 150),
0 - G a - 0 101.7(3)-106.3(4) (av 104).
R. A. Kovar, H Derr, D. Brandau, J. 0 . Callaway, Inorg. Chem. 1975, 14,
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teXsan: Crystal Structure Analysis Package, Molecular Structure Corporation, 1992
A Cage Molecule with a Cubanoid P4B4
Framework: tBu4P4Ph4B40,,-A Structural
Analogue of the Isovalence Electronic
OrganosilasesquioxanesRSSisO,
Klaus Diemert, Ulli Englert, Wilhelm Kuchen,* and
Frank Sandt
Whereas a large number of oligomeric compounds with a
Si-0-Si framework is known, to our knowledge no materials
have hitherto been reported, which instead contain isovalence
electronic P-0-B groupings. Such materials could, however,
provide information as to whether substitution of this kind leads
to structures that are analogous to those of the S i - 0 compounds, as is the case for the solids SiO, and BPO,, and as to
how this substitution influences the physical and chemical properties of the substances. We have now found a way to couple
P-0-B bonds under mild conditions; this has afforded the title
compound 1, and possibly will facilitate the access to other
compounds from this class of substances.
Prior to this was our finding that phosphonic silyl esters
RP(O)(OSiMe,), react smoothly with phosphonic dichlorides
RP(O)Cl, under elimination of Me,SiCl to give phosphonic
anhydrides [RP(O)-O],, for which we postulated ring structures. For the substituents R = tevt-butyl, 2-methylphenyl, and
2,4,6-trimethylphenyl, we obtained trimers, among which the
tert-butyl compound is remarkably stable to hydrolysis. Therefore, not only was it possible to follow its stepwise degradation
via the corresponding tri- and diphosphonic acids to the phosphonic acid, but the intermediates could be isolated as such or
as salts."' 1'
We have now treated the tert-butylphosphonic bis(trimethyisilyl ester) with PBCl, in toluene according to Equation (a) and obtained the mixed anhydride l , which forms colorless, moisture-sensitive needles that melt above 300 "C with
decomposition and dissolve readily in benzene, toluene, and
chlorohydrocarbons.
4fBuP(O)(OSiMe,), +4PhBCI,
-Me,SiCI
fBuPuPh4Bu0,,
(a)
1
According to the crystal structure analysis,[311 did not have
the 16-membered ring structure [P(tBu)(O)-0-B(Ph)-01,
which we had initially expected. Instead 1 revealed a cage structure with a cubane framework, the corners of which are occupied alternately by P and B atoms. The 12 0 atoms are located
approximately in the middle of the edges. Thus, each P and each
B atom is tetrahedrally coordinated by the respective organic
group and three 0 atoms (Figure 1). In the crystal lattice the
centers of gravity of each molecule occupies the corner or center
of slightly distorted cubooctahedra. Figure 2 shows the central
P,B,O,, framework of a molecule surrounded by the center of
gravity of each its twelve neighboring molecules.
The phosphorus-oxygen and boron-oxygen bonds in 1 are
largely equivalent. The average P - 0 distance of 1.502 8, (12
values, 1.486(3)-1.516(3) A) lies in the range typical for partial
[*I Prof. Dr. W. Kuchen, Dr. K. Diemert, Dr. F. Sandt
Institut fur Anorganische Chemie und Strukturchemie I der Universitat
Universitatsstrasse 1, D-40225 Dusseldorf (Germany)
Fax: Int. code +(211)81-12287
Dr. U. Englert
Institut fur Anorganische Chemie der Technischen Hochschule
Prof.-Pirlet-Strasse 1, D-52074 Aachen (Germany)
Fax: Int. code +(241)8888-288
Angew Chem. Ini. Ed. Engl. 1997, 36, No. 3
0 VCH
Verlugsgesellschuft mbH, 0-69451 Weinheim, 1997
0570-0833j97/3603-0241$ IS.OO+ .2S/0
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gallium, thein, structure, motifs, molecular, cyclic, organophosphonates, gallophosphate, sieve, relationships, cubic
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